This invention relates generally to power generation, and more specifically, to methods and apparatus for assembling solid oxide fuel cells.
At least some known power generation systems use fuel cells to produce power. Known fuel cells typically include an anode, also known as a fuel electrode, a cathode, also known as an oxidant electrode, and an electrolyte. Such fuel cells are electrochemical devices, similar to batteries, which react fuel and oxidant to produce electricity. However, unlike batteries, fuel such as hydrogen and oxidant such as air are supplied continuously to the fuel cell such that it continues to produce power so long as such reactants are provided.
A fuel cell produces electricity by catalyzing fuel and oxidant into ionized atomic hydrogen and oxygen at, respectively, the anode and cathode. The electrons removed from hydrogen in the ionization process at the anode are conducted to the cathode where they ionize the oxygen. In the case of a solid oxide fuel cell, the oxygen ions are conducted through the electrolyte where they combine with ionized hydrogen to form water as a waste product and complete the process. The electrolyte is otherwise impermeable to both fuel and oxidant and merely conducts oxygen ions. This series of electrochemical reactions is the sole means of generating electric power within the fuel cell. It is therefore desirable to reduce or eliminate any mixing of the reactants, as such mixing would result in a different combination such as combustion which produces no electric power and therefore reduces the efficiency of the fuel cell.
Individual fuel cells produce power at low voltage, typically about 1 Volt per cell. The cells are therefore typically assembled in electrical series in a fuel cell stack to produce power at useful voltages. To create a fuel stack, an interconnecting member is used to connect the adjacent fuel cells together in electrical series. Often the interconnecting member also performs the function of separating the reactants flowing through the fuel cell stack. The number of fuel cells that may be coupled together and/or an operating efficiency of the fuel stack may be adversely impacted by the interconnecting member. For example, at least some known fuel cell interconnecting members may not adequately maintain a separation of the reactants flowing through the fuel cell when the fuel cell is operated at high temperatures, such as between approximately 600° Celsius (C.) and 1000° C.
To facilitate maintaining the separation between reactants, at least some known fuel cells have seal assemblies. For example, at least some known fuel cell seals are fabricated using glass or glass ceramics, however glass or glass-ceramic seals may not be reliable under thermal cycling. Other known fuel cells have seals fabricated using mica materials, metallic, ceramic or composite materials. Although such seals generally withstand the thermal cycling better than the seals fabricated with glass, such seals have not proven to provide substantially leak tight seals.